1. Field of the Invention
The present invention relates to a method for the transmission of user data between military aircraft via antennas with controllable directional effect and a device for carrying out the method.
2. Discussion of Background Information
With data exchange between military aircraft, it is of the greatest importance that they are not discovered in an environment threatened by enemy reconnaissance systems. Military aircraft have been hitherto equipped for data transmission with omnidirectional antennas that essentially transmit and receive in the azimuth range and in the elevation range are active only in a limited angular range.
Very high powers are necessary to transmit user data via these omnidirectional antennas. This is because the data transmission takes place in a broadband manner due to the size of the data quantities. Moreover, transmission with omnidirectional characteristics can be realized only with high-energy expenditure. This results in a very unfavorable ratio between the locatability range and the transmission range. Usually a minimum transmitting power of 1 watt is necessary, resulting in a transmission range for the user data of approximately 50 km. In this case, however, the transmitting aircraft is locatable from a distance of approximately 1000 km.
Furthermore, directional antennas are known from the prior art, i.e., antennas that produce pivoting antenna main lobes for transmitting and receiving. Since the radiation is also emitted essentially in the azimuth range, and thus only a small antenna surface is available on the aircraft, these directional antennas have a very unfavorable ratio between the locatability range and the transmission range that results in a range between 0.5 and 5. Usually with these directional antennas, a user data transmission range of 100 km and a locatability in the range of 50 km is still achieved, if the enemy reconnaissance system is located outside the antenna main lobe. However, these relative sizes are obtained only with a special so-called power management, i.e., with a transmitting power adapted to the conditions and in particular to the distances between the transmitting and receiving aircraft.
Furthermore, user data transmission systems are known from the prior art in which satellites are used as relay stations. The user data has to be transmitted with great power due to the very great transmission range, so that a great locatability range occurs.
Furthermore, delays in the transmission time have to be taken into consideration. If geostationary satellites are not used, several such relay stations may be necessary, which is associated with higher costs.
An antenna orientation arrangement for an aircraft is known from DE 198 53 933 A1, which arrangement is connected to an attitude reference system of the aircraft in order to control the orientation of the antenna lobe.
The constellation shown in FIG. 1 of a low-flying transmitting aircraft 1 and a high-flying receiving aircraft 2, and a locating station 3 to be regarded as hostile with respect to the aircraft shown, shows in a diagrammatic manner a situation in a reconnaissance mission in enemy territory as shown according to the prior art. The antenna diagrams or characteristics of the transmitting aircraft 1 and of the receiving aircraft 2 resulting from the customary omnidirectional antennas are shown diagrammatically and labeled with reference numbers 1a or 2a. 
In a threat scenario, the locating station 3 is able to detect electromagnetic rays and to determine their direction. This can take place, if necessary, in interaction with other locating stations. The locatability increases with the transmitting power of the aircraft 1 respectively transmitting user data. The aircrafts position can then be determined with great precision through customary methods such as, e.g., triangulation with several such locating stations 3.